Basal body reorientation mediated by a Ca2+-modulated contractile protein

Area of Science:

• Cell Biology
• Algal Physiology
• Biophysics

Background:

• Flagellated green algae exhibit a photophobic response, involving a rapid, calcium-dependent change in basal body angle.
• This response is crucial for motility and survival in changing light conditions.

Purpose of the Study:

• To investigate the mechanism of basal body reorientation during the photophobic response in Spermatozopsis similis.
• To identify the molecular components responsible for calcium-induced basal body movement.

Main Methods:

• Isolation and reactivation of flagellar apparatus complexes from Spermatozopsis similis.
• Manipulation of calcium ion (Ca2+) concentrations and inhibition of flagellar beating.
• Immunofluorescence and immunogold electron microscopy using antibodies against a known contractile protein.
• Electrophoretic and immunoblot analysis of flagellar apparatus proteins.

Main Results:

• Calcium ions (≥ 10(-7) M) induce basal body reorientation and alter flagellar beat patterns in isolated flagellar apparatuses.
• Basal body reorientation occurs independently of flagellar beating.
• The distal basal body connecting fiber of Spermatozopsis similis is immunoreactive with an antibody against a 20-kD contractile protein.
• This protein consists of two acidic isoforms of 20 kD, similar to the protein in Tetraselmis striata.

Conclusions:

• The distal basal body connecting fiber acts as a contractile organelle.
• This contractile fiber is responsible for reorienting basal bodies during the photophobic response in certain flagellated green algae.
• The findings elucidate a novel contractile mechanism underlying cellular responses to environmental stimuli.